1. Field of Invention
The present invention relates to systems and methods for operating a traveling spark ignitor for use in an internal combustion engine and, more particularly, to systems that operate in two or more different mode of operation depending upon the current operating conditions of the engine.
2. Related Art
There exist several types of ignition systems for creating a spark to ignite a fuel/air mixture in combustion chamber of an internal combustion engine. A conventional ignition system typically provides a single high voltage capable of causing a discharge between the two electrodes of a conventional spark plug. Common systems for providing such a high voltage include transistorized coil ignition (TCI) and capacitive discharge ignition (CDI) systems. These systems are affective in providing the required high voltage for the initial discharge.
However, recent study has shown that spark plugs which are capable of producing a volume of plasma between the electrodes and expelling the plasma into a combustion chamber may produce better ignition efficiency as well as reducing the amount of hydrocarbon emissions of an internal combustion engine. Such spark plugs are driven by dual-stage electronics with provide an initial high voltage pulse that causes a breakdown between the electrodes to create an initial plasma kernel. A follow-on low voltage high current pulse is then provided which creates a current through the plasma. The location where the current travels through the plasma is swept outward, along with the plasma, under Lorentz and thermal expansion forces. Examples of such a spark plug as well as the associated dual stage electronics which operate in this manner are disclosed in U.S. Pat. No. 5,704,321 and U.S. patent application Ser. No. 09/204,440, both of which are hereby incorporated by reference.
The Traveling Spark Ignition (TSI) disclosed in U.S. Pat. No. 5,704,321 has been shown to provide multiple benefits for engine operation. The effect on operation is particularly strong when the engine is faced with inhomogeneous, highly variable or poorly-mixed fuel/air mixtures. These conditions may occur in engines having a carburator operating at low RPM""s in lean-running engines (particularly when using a high degree of exhaust gas recirculation), and in direct-injected engines running in stratified-charge mode.
Research has shown that the beneficial effects of a large but short-lived ignition kernel are particularly strong when fuel/air mixture speeds within the engine cylinder are low (see, e.g., xe2x80x9cIgnition Systems for Highly Diluted Mixtures in SI-enginesxe2x80x9d by Robert Boewing et al., SAE paper No. 1999-01-0799, which is hereby incorporated by reference). Further benefits of this system derive directly from the larger ignition kernel: at extremely high speeds, engine operation is actually limited by the speed of flame-front propagation, and a TSI system is able to speed up burn at this speed (important for racing applications) and incrementally push up vehicle speed. At higher flow rates (achieved partially by good engine design, but mainly a result of higher engine speeds), or when the mixture is highly homogeneous and near stoichiometric, a smaller but longer-duration spark may be almost as effective in producing consistent ignition. The effectiveness of the smaller, longer-duration spark may be a result of the xe2x80x9ceffective surface areaxe2x80x9d of the ignition kernel growing rapidly as fuel/air mixture flow speeds increase.
Electrode wear has been a chronic problem in high-energy plasma ignition systems. Early dual-energy ignition experiments using plasma-jet plugs or electromagnetic rail plugs showed a high rate of electrode wear.
In one embodiment, the present invention relates to a system that delivers the benefits of TSI under difficult engine operating conditions (i.e., inhomogeneous fuel/air mixtures) and at the same time conserves energy and extends its own life through dual modes of operation which allow the ignitor to function either as a TSI or conventional ignition device, depending on the operating regime of the engine. In addition to providing this function for original equipment manufacturer engines (where the ignition system is installed in the factory), the present invention is well-suited to manufacturing add-on modules mounted by users for the after-market.
To function in a dual-mode environment, the plug portion of the system may be designed as to ignite the fuel/air mixture effectively and consistently in both conventional and TSI modes of operations. In conventional ignition operation, a conventional high-voltage ignition system (usually a capacitive-discharge ignition or a transistorized-coil ignition) produces and sustains a spark at a breakdown area between plug electrodes. The small strand of plasma provides effective ignition if the fuel/air mixture is well homogenized and/or flowing rapidly past the spark (so that the ignition kernel effectively xe2x80x9ctouchesxe2x80x9d as much fuel/air mixture as possible). When engine conditions make consistent fuel/air ignition difficult (when the fuel/air mixture is lean, mixing is poor, or fuel quality is poor) it may be preferable to have the plug perform in a traveling-spark mode which maximizes the size of the ignition kernel for a given amount of energy.
In one embodiment, a system for providing electrical energy to a traveling spark ignitor operating in an internal combustion engine is disclosed. The system of this embodiment includes a conventional ignition system connected to the ignitor and a follow-on current producer which produces a follow-on current that travels between electrodes of the ignitor after an initial discharge of the conventional ignition system through the ignitor. The system of this embodiment also includes a disabling element that prevents the follow-on current from being transmitted to the ignitor. In some aspects of this embodiment, the disabling element may prevent the follow-on current from being transmitted to the ignitor based upon current operating conditions of the engine.
In another embodiment, an electrical firing circuit for firing a traveling spark ignitor that may be used in an internal combustion engine is disclosed. In this embodiment, the circuit includes a conventional ignition system connected to the ignitor that produces a first discharge between electrodes of the ignitor and a secondary circuit that produces a second discharge between the electrodes following the first discharge. This embodiment also includes means for disabling the secondary circuit when the engine is operating in a first condition.
In another embodiment, a method of controlling ignition circuitry for a traveling spark ignitor operating in a combustion engine is disclosed. The method of this embodiment include steps of receiving a signal representing an operating condition of the engine and disabling a portion of the ignition circuitry if the engine is operating in a first mode.